I think that having a photographer review, especially for paid photoshoots is a great idea. It is a business transaction, and you should have the right to know if there are other people that have had problems with that person before. I also think that if you are paying the cosplayer, monetarily or otherwise, you should have the right to know if they are difficult to work with as well.
Is Cosplay.com the best place for it? Perhaps not, but I do think that when you are going to spend the money to work with someone that you do not know, you want to feel comfortable that you are going to be safe with that person, especially if you are going to be meeting at a Con. Since payment for photoshoots isn't allowed in most Con areas, you are likely to travel outside of the Con area to a less trafficked area to take the pictures so you want to feel safe.
In regards to word of mouth, people are now traveling farther to go to Cons, it's not just in your immediate circle. It's a lot harder to know if someone has a good reputation if they are on the other coast.
The word of mouth ties into the "tell the con staff" in that it's only a short term solution and unless you spend every waking moment telling everyone you know about the experience you had, it is likely to happen again some other time to someone else if you weren't just an isolated incident and there is no way to make the knowledge public in a lasting, searchable fashion.